Severe decline in performance and tab crashes.

These would get submitted and parsed, so if you check they got uploaded and paste a few of the crash IDs here to check if there's pattern perhaps?

1. Enter about:crashes in the Firefox address bar and press Enter. A list of Submitted (and Unsubmitted, if any) Crash Reports will appear, similar to the one shown below.
2. Copy the 5 most recent Submitted Report IDs that start with bp- and then go back to your forum question and paste those IDs into the "Post a Reply" box.

Note: If a recent Report ID does not start with bp- click on it to submit the report.

(Please don't take a screenshot of your crashes, just copy and paste the IDs. The below image is just an example of what your Firefox screen should look like.)

More information and further troubleshooting steps can be found in the Troubleshoot Firefox crashes (closing or quitting unexpectedly) article.

bp-6050241a-9d03-4a48-b212-24e260260626 bp-872a2693-5133-45b9-a644-b629b0260621 bp-36a1d4d5-bc32-4f03-9cea-91d9a0260621 bp-1e76743a-6ffb-4ccf-83df-9cdea0260617

Those are just a handful, but I've got 45 crashes from this month. I could swear it's been crashing more than even that though.

So these all appear as some long–running streams, like streaming for days.

What happens if you restart into Troubleshoot Mode via the Help menu, and do not leave Youtube content open running, streaming and chats open for days — does the stability change?

(Which doesn't match the uptime in the logs captured though; wondering if any addon can exacerbate this.)

Would you be willing to make a new temporary profile on the side, and ideally not log into G/YT in it so they can't target you with potentially the same experiment or rollout variant, and try using that fresh "clean slate" for a bit to compare? Thanks.